The Nth Prime Number
Enter a value for n below, from 1 to 10^12, inclusive. The server will return the nth prime number (counting 2 as the first). Commas and scientific notation (e.g. 1.0e12) are allowed.http://primes.utm.edu/nthprime/index.php#nth

Factorise
Visualize factors through building rectangular areas on a grid. First enter all the factorizations of a number, then draw each factor set as an area on the grid. Factorize is one of the Interactivate assessment explorers.

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board? But there is a twist - you also have to click on the 'odd number out'!

A highly interactive Promethean ActivBoard flipchart where students discover the prime numbers, factors of numbers and the Highest Common Factor using a game based on Eratosthenes Sieve. Three thumbs up!